As a core technology of a next-generation transport network, an optical transport network (OTN) has rich operation, administration and maintenance capabilities, a powerful tandem connection monitoring capability, and the like, and can implement flexible scheduling and management on large-capacity services.
The OTN technology defines a standard frame structure to map various client services. First, an optical channel payload unit (OPU) overhead is added to a client service to form an optical channel payload unit-k (OPUk), and then the OPUk is encapsulated, an optical channel data unit (ODU) overhead is added to form an optical channel data unit-k (ODUk), and then an optical channel transport unit (Optical Channel Transport Unit, OTU) overhead is added to the ODUk to form an optical channel transport unit-k (OTUk). k=1, 2, 3, and 4, which are corresponding to four fixed rate levels, namely, 2.5 Gbit/s, 10 Gbit/s, 40 Gbit/s and 100 Gbit/s respectively.
With a massive growth of service traffic, to fully utilize bandwidth resources of the OTN, currently, the Study Group 15/International Telecommunication Union-Telecommunication Standardization Sector (Study Group 15/International Telecommunication Union-Telecommunication Standardization Sector, SG15/ITU-T) is discussing to develop an optical channel transport unit-Cn (OTUCn) signal with a flexible line rate. A bit rate of the OTUCn signal is n multiples of a reference rate, and n is variable, where the reference rate may be preferably a rate at a rate level of 100 Gbit/s, and the foregoing C is the number “100”. Corresponding to the OTUCn signal, there are an optical channel data unit-Cn (ODUCn) signal and an optical channel payload unit-Cn (OPUCn) signal. The OPUCn signal may be split into 10n 10 G tributary slots, to implement hybrid carrying for multiple low-order services. Because various low-order services occupy tributary slots (TS) of the OPUCn randomly, tributary slot fragments may exist in the OPUCn signal, or after some low-order services are canceled, tributary slot fragments may also exist in the OPUCn signal. Because of the existence of these tributary slot fragments, network bandwidth resources cannot be allocated according to requirements of actually carried low-order ODU services, which decreases utilization of the network bandwidth resources.